1. Field of the Invention
The present invention relates generally to the field of cellular communications, and more particularly to a method for optimizing power consumption at a mobile station by minimizing mobile terminal searching for a home network.
2. Description of the Related Art
Mobile and cellular phones have enabled mobile station users to roam over large geographic areas, while also providing the flexibility to carry different types of information over a single system. Mobile stations include portable units such as, for example, cellular phones, mobile phones and like, which can be used to transmit digitized sound, text, data, digital video or other information existing in digital form. Cellular communication systems typically provide service to a geographic area by dividing the geographical area into adjoining sections called Public Land Mobile Networks (PLMNs). The boundaries of the sections are often determined by, for example, size, geographical features, population density, or national borders. Every PLMN is further subdivided into cells, where each cell is serviced by a radio transceiver. Cells can be visualized as small geographical zones covering the region. These zones, or cells, are joined to completely blanket the PLMN. Each cell has an allocation of distinct frequencies for communication with the mobile station. The frequencies of adjoining cells are different to prevent radio interference between mobile station users in adjoining cells.
A mobile station is also free to roam. Specifically, the mobile station is allowed to operate as it travels through a variety of geographical regions. To ensure the existence of adequate communication, the mobile station will change cells and communicate with proximate cells as it moves. It is common for wireless communications network operators to offer service plans, for example, nationwide calling plans, with coverage in geographical areas that are served by third party network operators, and not a home operator's network. The home operator generally shares agreements with other network operators in order to provide service to subscribers in areas where the home operator does not actually own and operate network infrastructure.
When the user of a mobile station has a dedicated channel for communication with other phone users, decisions regarding which cell to communicate through are made at the network level. However, when the mobile station does not have a dedicated channel, the mobile station has more authority in deciding which cell it considers itself to be located. The mobile station constantly monitors the power level of radio signals transmitted by neighboring cells. Based on the monitored power levels, and information received from the cells, the mobile station makes a decision regarding which cell it is located. By choosing a particular cell, the mobile station simultaneously selects the PLMN to which the cell belongs. The selection of a particular cell can be based on a ranking of neighboring cells.
In addition to searching for neighboring cells, the mobile station also searches for its Home Public Land Mobile Network (HPLMN). The HPLMN is the network with which the mobile user has a subscription relationship, and the network with which the mobile user prefers to do business. In the automatic network selection mode, the mobile station automatically attempts to select and register with the HPLMN.
Generally, the mobile station makes attempts to return to its HPLMN when visiting another PLMN. A roaming mobile station periodically scans for its home network. The network scanning procedure consumes power, which significantly reduces battery life compared to the power consumed when the mobile station is not roaming and scanning for its home network. Reduction of battery life reduces the length of time that the mobile station can be operated before its battery is depleted.
It is also desirable for the mobile station user to communicate through their HPLMN in order to reduce call costs. When the mobile station uses other PLMNs charges may vary, and the user may be unaware of higher costs as the call is being made. It is possible for the mobile station to acquire another PLMN, other than the HPLMN, as it travels, and remain with this network long after the mobile station has moved back within range of the HPLMN. As a result, mobile stations may visit PLMNs other than the HPLMN more often than is necessary.
Networks may specify a list of equivalent PLMNs that recipient mobile stations may treat as though the equivalent PLMNs belong to the same network. Hence, a mobile station will not perform periodic HPLMN searches when camped on networks that are equivalent to the HPLMN of the mobile station. However, rendering the equivalent PLMN feature is substantially currently unavailable. Further, the equivalent PLMNs feature is dependent upon competing network operators configuring network information in a manner that reduces unnecessary HPLMN searching by roaming mobile stations. If there is no indication that the roaming PLMN is equivalent to the mobile station's HPLMN, the roaming mobile station will continue searching for its HPLMN.
The mobile station performs a search even when the network topology is not changing due to limited mobility, and when and there is no possibility of finding the HPLMN. Further, the mobile station can get stuck in a limited service state. Still, the mobile station does not change its scanning rate based on the perceived rate of change of network topology by the mobile station, which leads to high power consumption by the mobile station in limited service state.
Further, signal strength alone is not a reliable way to determine movement of the mobile device. For example, signal strength can change based on a vehicle passing near the mobile device. Thus, changing of a scan rate should not be based only on a fixed signal strength threshold.
The aforementioned techniques utilize a large amount of battery power of the mobile station while performing excessive searches for an HPLMN.